1. Field of the Invention
The present invention relates to an image input apparatus and in particular, to an image input apparatus for inputting a monochromatic image and a color image of a portion of a postal matter to which light is applied from a light source, thereby recognizing the postal matter for the area division.
2. Description of the Related Art
This type of image input apparatus is generally mounted on a so-called flat apparatus for recognizing postal matters having a size out of a predetermined range (hereinafter, referred to as a flat mail classification apparatus). The conventional flat mail classification apparatus uses an image input apparatus for reading an entire image on a flat mail surface as a monochromatic image of a fine resolution capable of recognizing characters, so that an address is recognized from the image information for the area division of the flat mail.
However, a flat mail has a large area to be processed as compared to a normal mail size and it is often a case that a complicated design or characters are printed beside the address. Accordingly, when a format of a high resolution is used, the information amount of the monochromatic image becomes enormous, requiring a plenty of time for recognizing only the address from that information.
It is therefore an object of the present invention to provide an image input apparatus for use in a flat mail classification apparatus for detecting an address area by using a color information and performing a character recognition to that area, thereby enabling to obtain a high-speed flat mail classification.
The present invention provides an image input apparatus comprising: feed means for feeding an object in a constant direction; illumination means having a light source for applying light rays toward the object fed by the feed means in the constant direction and a filter for cutting heat rays from the light source while allowing visible light rays to pass through; monochromatic and color pickup means for picking up the object illuminated by the light rays with a linear field of view intersecting the feed direction; and cooling means for forced cooling by generating an air flow between the illumination means, the light source, and the filter, wherein the monochromatic pickup means has a high resolution appropriate for a character recognition and the color pickup means has a low resolution appropriate for a character area detection.
Images are taken in from the same position by the monochromatic pickup means having a fine resolution sufficient for a character recognition and the color pickup means having a rough resolution sufficient for an address area detection. The address area is detected by the color image and a character recognition process is performed only to that area by using the monochromatic image of the high resolution, thereby enabling to obtain a high-speed character recognition, increasing the speed of the flat mail classification. The address area often has a color different from the flat mail itself or other pattern. Accordingly, the address area detection based on the rough color information is advantageous.
Moreover, since the illumination means is provided with the cooling means for forcibly cooling the light source and the filter by generating an air flow, it is possible to use a high-output light source accompanied by heat rays, reducing the CCD exposure time for assuring the necessary S/N ratio. This further increases the speed of the flat mail classification. Furthermore, since it is possible to obtain a sufficient illumination depth of luminance, it is possible to cope with flat mails having different thickness values.
Especially when the illumination means 1 is realized by a single unit, it is preferable that the illumination means, the feed means, and the pickup means be arranged in such a manner that the illumination unit has its optical axis forming an acute angle against the feed direction of the feed means and the angle is different from an angle defined by the optical axis of the monochromatic and color optical axis of the pickup means and the feed direction of the feed means.
This provides an advantage that it is possible to prevent halation caused by the light rays from the illumination means which is mirror-reflected directly from an object on the feed means to be introduced into the pickup means.
Moreover, when the illumination means is realized by two illumination units, they are arranged so as to sandwich the linear field of view of the pickup means.
Similarly as described above, it is possible to prevent halation caused by the light rays from the illumination means which is mirror-reflected directly from the object on the feed means and introduced into the pickup means.
The illumination means may use as the light source a high pressure sodium lamp.
Although the high-pressure sodium lamp is accompanied by heat rays, the heat rays may be removed by a heat ray cut filter and the heated lamp itself can be sufficiently cooled by an air flow.
The pickup means preferably has the monochromatic optical path and the color optical path which are approximately vertical to the feed direction of the feed means and are positioned in the proximity to each other along the feed direction of the feed means.
When the monochromatic optical path is in the proximity to the color optical path, it is possible to reduce an address area detection error to a value that can be ignored. This eliminates need to perform an operation required for matching the fields of view of the monochromatic image and the color image taken in, thereby enabling to perform a character recognition based on the address area detection at an increased speed.
Furthermore, it is possible to constitute the configuration such that the pickup means has its monochromatic optical path and color optical path which are overlapped in the first half of the optical path from the pickup surface to the focusing means and then branched by optical path branching means so as to be introduced to monochromatic focusing means and color focusing means of the pickup means, respectively.
Moreover, the pickup means may include a plurality of mirrors for refracting the optical paths so as to prolong both of the chromatic optical path and the color optical path within a limited space.
When the optical path is prolonged, it is possible to suppress magnification fluctuations caused by movement of the pickup surface, thereby enabling to cope with flat mail thickness fluctuation, which in turn improves the character recognition accuracy.
Furthermore, the pickup means preferably includes a polarization filter and a infrared ray cut filter which are arranged in the monochromatic optical path, and a color correction filter, a polarization filter and an infrared ray cut filter which are arranged in the color optical path.
The polarization filter removes the mirror reflection from a flat mail wrapped in a material easily causing a mirror reflection such as vinyl and increases the substantial contrast of the image to improve the character recognition accuracy. Moreover, the infrared ray cut filter cuts off near infrared rays remaining in the reflected light and increases the contrast of characters written with ink such as a ball-point pen, thereby improving the character recognition accuracy. Furthermore, the color correction filter serves for rough correction of the color balance.
The pickup means has its monochromatic field of view and color field of view having an identical width, and only their resolutions are different.
More specifically, the monochromatic pickup means has a high resolution appropriate for a character recognition while the color pickup means has a resolution low but sufficient for an address area detection. This enables to reduce the processing time required for the address area detection and the character recognition as well as to improve the character recognition accuracy.
The pickup means preferably includes independent focusing means, photo-electric conversion means, video signal processing means, and image data transfer means for each of the monochromatic pickup and the color pickup.
This configuration enables to perform the image processing of the monochromatic image and the color image substantially simultaneously, thereby enabling to reduce the processing time required for the address area detection and the character recognition. This significantly increases the flat mail classification work.
The photo-electric conversion means includes a linear array CCD consisting of light receiving elements arranged in a straight line for monochromatic image pickup and a linear array CCD consisting of light receiving elements arranged in a straight line for color image pickup, and further includes shading means for shading a part of the monochromatic and color linear array CCD.
Thus, by shading a part of the monochromatic and color linear array CCD, it is possible to obtain pickup means having a linear field of view by utilizing ordinary linear array CCD available on market. Moreover, by performing pickup with a linear field of view, it is possible to reduce the data transfer amount and increase the speed of the entire processing flow. It should be noted that in principle a portion of the CCD which is transferred later is shaded.
Moreover, the monochromatic-mode video signal processing means may include envelope detection means and analog/digital conversion means; and the color-mode video signal processing means includes analog/digital conversion means and image correction means.
The envelope detection means detects a background luminance as a reference level so as to digitize the monochromatic image. This enables to obtain a clear image by substantially eliminating the illumination irregularities due to the illumination means and the exposure shortage (shading) at a peripheral portion of the lens, thereby improving the character recognition accuracy. Moreover, the color-mode vide signal processing means is provided with the image correction means for performing a correction process to the image data converted into a digital data. This enables to perform the light distribution correction and the white correction (white balance adjustment), thereby assuring the address area detection.
Furthermore, the envelope detection means may include correction means for correcting distortion of a video signal when the object caused mirror reflection.
This correction means includes: a function to detect a luminance increase of a background due to a mirror reflection of an object and to reduce a time constant of the envelope and a function to detect that the background luminance has returned to a normal state and return the time constant of the envelope to a previous state. When a mirror reflection is caused in the object to increase the luminance, the reference level is increased to compress the contrast, which is disadvantageous for character recognition. However, since this period of time can be reduced by reducing the time constant, it is possible to improve the character recognition accuracy as a whole.
Moreover, the image correction means for color pickup may include correction data generation means for calculating a correction data with respect to a reference signal which has been converted into a digital signal by the photo-electric means and the analog/digital conversion means using a reference plate as the object and writing the calculation result into a storage device.
This enables to maintain correction data related to the light distribution correction and the white correction, thereby eliminating need to frequency calculate correction data. Thus, it is possible to significantly improve the entire work efficiency. In order to always have an optimal correction data, it is preferable to periodically calculate the correction data and write the calculation result in a storage device.
Furthermore, the image correction means for the color pickup may include correction data read-out means for reading out the correction data from the storage device using the object image data which has been converted into a digital signal by the analog/digital conversion means, as a part of an address value of the storage device.
With this configuration, it is possible to read out a correction data from the storage device, corresponding to an address of the object image data, i.e., a portion of the pickup image. This enables to automatically perform image corrections such as the light distribution correction and the white correction.
The correction data generation means includes a calculation function to perform a smoothing process to remove stains on the reference plate and noise of a circuitry from the reference signal for a curve approximation process of the illumination light distribution characteristic and to unify the reference values after the correction for respective colors, thereby simultaneously performing the light distribution correction and the white correction.
With this function, it is possible to eliminate noise caused by stains on the reference plate, irregularities of the CCD sensitivity and the light reception characteristics, aberrations of the optical system arranged in the pickup means, and the like, thereby enabling to obtain an appropriate correction data.
Moreover, the calculation function may include an error detection function for detecting irregularities of the light distribution characteristic obtained by the curve approximation to detect an error of the reference plate and the circuitry and output an error signal.
With this error detection function, it is possible to detect a significant failure in the reference plate and the circuitry, thereby preventing an error due to use of an improper correction data.
The smoothing process for noise removal may be performed by a median processing and the curve approximation process of the light distribution characteristic may be performed by a three-dimensional spline interpolation.